Controlling apparatus of a reactor

ABSTRACT

A batch reactor is controlled by measuring heat transfer to or from the reactor and integrating the measured signal. When the integrated signal reaches a preselected value, the reaction is terminated. The integrated signal can also be used to control introduction of a reactant.

United States Patent Hoffman, Jr.

[ 1 Feb. 29, 1972 CONTROLLING APPARATUS OF A REACTOR Alfred A. Hoffman,Jr., Bartlesville, Okla.

Assignee: Phillips Petroleum Company Filed: July 18, 1969 Appl. No.:843,158

Inventor:

U.S. Cl ..23/253 A, 23/230 A, 23/1 B, 165/12, 165/30, 165/36, 165/39,137/2, 137/90, 222/52, 260/700 Int. Cl. ..G0ln 25/42 Field ofSearch..23/253, 1 B; 165/2, ll, 12, 165/30, 36, 39, 40

References Cited UNITED STATES PATENTS 2,788,264 4/1957 Bremer et a1..23/1 B X 2,909,413 10/1959 Hildyard ..23/253 UX 3/1961 Morgan ..23/253Primary ExaminerJames l-l. Tayman, Jr. AttorneyYoung and Quigg [5 7]ABSTRACT A batch reactor is controlled by measuring heat transfer to orfrom the reactor and integrating the measured signal. When theintegrated signal reaches a preselected value, the reaction isterminated. The integrated signal can also be used to controlintroduction of a reactant.

5 Claims, 1 Drawing Figure HEATER CONTROLS 99 INTEGRATOR 15 e2 26 as 97-MULTIPLIER CONTROLLING APPARATUS OF A REACTOR lt is common practice inthe chemical industry to carry out various chemical reactions in batchreactors. In order to ob tain maximum production of specificationproduct, it is usually necessary to control quite accurately both therate of additionof reactants and the termination time of the reaction.While automatic control can be based on a predetermined time sequence,process variations cannot be corrected during individual reactions bythis procedure. Another possible control method involves periodicremoval of samples from the reactor for analysis. However, certainreactants cannot be analyzed rapidly so that control systems based onanalyses are not always practical.

In accordance with the present invention, a control system is providedwhich is capable of determining automatically the rate at which achemical reaction takes place and the time at which the reaction iscompleted. This control is based on a measurement of the rate at whichheat is liberated in an exothermic reaction or the rate at which heat isabsorbed in an endothermic reaction. The heat transfer can be measuredby determining the rate of flow of a fluid passed in heat exchangerelationship with the reactor and the temperature differential of theheat exchange fluid upon entering and leaving the reactor. From thesemeasurements, an integrated signal is obtained which represents thecumulative heat change in the reactor, which is indicative of the degreeof completion of the reaction. This signal can be differentiated toprovide a control signal. This latter signal is independent of minorfluctuations in the heat exchange rate. In response to these signals,the reactor can be controlled by adjusting the rate of addition of oneor more reactants, and the reaction can be terminated at the propertime.

The accompanying drawing is a schematic representation of an embodimentof the control system of this invention.

In order to describe the control system of this invention, referencewill be made to a particular reaction for the production ofpolyphenylene sulfide. This polymer is produced by reactingdichlorobcnzene with partially hydrated sodium monosulfide in a batchreactor. The reaction is exothermic with a heat of reaction ofapproximately 1200 Btus per pound of polymer produced.

Referring now to the drawing in detail, there is shown a reactor 11which is provided with ajacket 14 through which a heat exchange mediumcan be circulated. Reactor 11 is provided with agitation means such as astirrer 13 which is rotated by a motor 12. A heat exchange medium isintroduced into jacket 14 through a conduit 15 and is removed through aconduit 16. The heat exchange medium is directed by a pump 17 fromconduit 16 through a conduit 18 which is connected to parallel conduits20 and 21, the latterjoining a conduit 22 at a valve 32. Parallelconduits 25 and 26 connect conduit 22 to inlet conduit 15 at a valve 37.Heat exchange medium is thus circulated in a closed loop whichincludesjacket l4.

Cooling means 30 and 36 are disposed in respective conduits 20 and 26,and a heater 31 is disposed in conduit 21. The temperature of the heatexchange medium introduced into jacket 14 can thus be regulated bymanipulation of valves 32 and 37 to control the relative flows throughthe cooling and heating means.

Dichlorobenzene is introduced into reactor 11 from a storage vessel 40which is connected to the reactor by a conduit 41 which has a valve 46therein. Partially hydrated sodium monosulfide is introduced intoreactor 11 from a storage vessel 42 which is connected to the reactor bya conduit 43 which has a valve 47 therein. At the beginning of areaction cycle, valves 46 and 47 are opened to introduce predeterminedquantities of the reactants into reactor 11. Product can be removed fromreactor 1] through an outlet conduit 48 which has a valve 49 therein.

A first temperature sensing element is positioned within reactor 11 tomeasure the temperature of the reaction medium. This sensing element isconnected to a transducer 70 which transmits a signal representative ofthe measured temperature to a temperature controller 71. A set pointsignal 72,

representative of the desired reaction temperature, is also applied tothe temperature controller. The output signal from controller 71, whichis representative of any difference between the measured signal and theset point signal, is transmitted as a set point signal to a secondtemperature controller 75. A second temperature sensing element ispositioned to measure the temperature of fluid in conduit 15. Thissensing element is connected to a transducer 74 which transmits a signalrepresentative of the measured temperature to controller 75. The outputsignal from controller 75, which is representative of the differencebetween the two input signals, is applied to valve 37 to adjust therelative flows through conduits 25 and 26. The output signal fromcontroller 75 is also applied as the input signal to a valve positioncontroller 78. Controller 78 receives a set point signal 79. The outputsignal from controller 78, which is representative of the differencebetween the two input signals, is applied to valve 32 to control therelative flows through conduits 20 and 21. The flow of heat exchangemedium through the closed loop is maintained at a predetermined rate bya flow controller which adjusts a valve 87 in conduit 18 in response toa signal from a transducer 86 which senses the rate of flow throughconduit 18.

As previously mentioned, the production of polyphenylene sulfide is anexothermic reaction. However, it is necessary to elevate the temperatureof the reactants to at least 400 F before the reaction will commence. Atthe beginning of the cy-- cle, the reactants are normally introducedinto reactor 11 at a temperature of approximately 350 F. In order tostart the reaction, warm heat exchange medium is circulated throughjacket 14. At this time, the signal transmitted by transducer 70 isrepresentative of a relatively low temperature within the reactor. Theoutput signal from controller 75 is such that valves 32 and 37 arepositioned so that all or at least a major portion of the heat exchangemedium flows through heater 31. This serves to elevate the temperatureof the reactor and start the reaction. As the reaction temperaturerises, it is necessary to convert from heating the reactor to coolingthe reactor in order to control the exothermic reaction. As the measuredtemperature within the reactor increases, the set point to controller 75changes so that valves 32 and 37 are adjusted to direct more of the heatexchange medium through coolers 30 and 36. In this manner, thetemperature of the reactor can be maintained at a desired set pointvalve during the reaction period, which may be of the order of severalhours. The reaction is advantageously carried out at a temperature ofapproximately 475 F.

A temperature sensing element is disposed in conduit 21 downstream ofheater 31 to measure the temperature of the heated exchange medium. Thissensing element is connected to a transducer 81 which transmits a signalrepresentative of the measured temperature to a temperaturecontroller'82. Controller 82 regulates a suitable heater control 83 inorder to prevent overheating of the exchange medium, particularly duringthe time that there is a low-flow rate through conduit 21.

In order to measure the rate of polymer production and to determine thetime at which the reaction is completed, signals are established whichare representative of the temperatures of the heat exchange mediumflowing into and out of reactor 11 and the rate of flow of this heatexchange medium. To this end, a first temperature sensing element ispositioned in conduit l5 adjacentjacket 14. This sensing element isconnected to a transducer which transmits a signal T, representative ofthe measured temperature to a differential temperature transmitter 93.Similarly, a transducer 91 transmits a signal T which is representativeof the temperature of the heat exchange medium removed through conduit16. A resulting signal representative of the quantity (TrT istransmitted as the first input to a multiplier 97. A flow transducer 95transmits a signal F to the second input of multiplier 97. Signal F isrepresentative of the rate of flow of heat exchange medium throughconduit 16. Multiplier 97 multiplies the two input signals andmultiplies the resulting product by a constant input signal K which isrepresentative of the specific heat of the heat exchange medium. Theresulting signal FK(T T,) is transmitted to the input of an integratorv99. Integrator 99 establishes an integrated output signal 110.Integrator 99 normally is set to begin integration at the start of thereaction cycle. Signal 110 is transmitted to a differentiating means 112which establishes an output signal 110/d0 that represents the derivativeof the integrated signal with respect to time. This signal istransmitted to the inputs of respective controllers 1 14 and 115.

Controllers 114 and 115 are provided with respective set point signals117 and 118. The output signal 124 of controller 114, which isrepresentative of the difference between the two input signals to thecontroller, is applied to a gate 136. When the gate is open, signal 124is transmitted to a flow controller 140 which adjusts a valve 141 in aconduit 43'. Conduit 43' extends from vessel 42 to the inlet of reactor11. The output,

signal 110 of integrator 99 is also transmitted to a controller 130which acts in an on-off manner. Controller 130, which receives a setpoint signal 133, establishes an output signal which opens gate 136 whena predetermined relationship exists between the two input signals tocontroller 130, as described hereinafter in greater detail. In a similarfashion, the output signal from controller 115 is applied to a timer126. The signal 125 from timer 126 is applied through a gate 137 tocontrol valve 49. This signal can also sound an alarm to alert operator.Gate 137 is controlled by a controller 131 which is similar tocontroller 130. Controller 131 receives signal 110 and a set pointsignal 134.

As previously mentioned, reactant initially is supplied from vessel 42through conduit 43. This is accomplished by opening valve 47 for apredetermined period. Thereafter, valve 47 is closed. However,additional reactant can subsequently be supplied through conduit 43. Atthe beginning of the reaction, integrator 99 is placed in operation tomeasure the exothermic heat of reaction. Initially, heat is supplied tothe reactor so that there is a negative, or zero, signal to theintegrator. At the beginning of the reaction period, gate 136 is closedso that there is no signal transmitted to flow controller 140. Valve 141remains closed at this time. The nature of the reaction is such that theproduction of polymer can be increased by adding additional reactantfrom vessel 42. This addition is controlled by the output signal fromdifferentiating means 112 which is applied through controller 114 tocontroller 140. The second input signal to controller 140 is from a flowtransducer 143. The set point of controller 130 is such that gate 136 ispermitted to open only after the reaction has progressed by apreselected amount, as indicated by the output signal from integrator99. This prevents premature addition of additional reactant.

it is normally desirable to limit the amount of reactant supplied fromvessel 42 during the course of the reaction. This is accomplished byflow transducer 143 transmitting a signal through an integrator 144 to aflow controller 145 which receives a set point signal 146. Controller145 serves to close valve 147 permanently when the total flow throughconduit 43 reaches a predetermined amount beyond the original reactant42 charge, as measured by the output signal from integrator 144.

At the start of the reaction cycle the temperature builds up to thedesired reaction temperature. The actual rate of reaction is measured bythe signal d/d6. When this signal reaches a predetermined value, asignal is transmitted through controller 115 to start timer 126. Timer126 is set to provide an output signal at the end of a predeterminedtime interval. This signal is applied through gate 137 to open valve 49,thereby draining the reactor. Controller 131 is provided with a setpoint such that gate 137 remains closed until the reaction has proceededto a specified level. This prevents the accidental opening of valve 49in the event that the signal from 112 should start the timer productionprematurely. Although not illustrated, the output signal from controller137 can be employed to initiate a new cycle by manipulation of valves 46and 47.

As a specific example of the control system of this invention, 4910pounds of dichlorobenzene at about 385 F are introduced into reactor 11from vessel 40. Then 3,!60 pounds of Na S-l.5H O are introduced fromvessel 42, together with 9,960 pounds of N-methyl-Z-pyrrolidone. Thesematerials are at an initial temperature of about 385 F. Hot'oil iscirculated through jacket 14 to elevate the temperature of thereactants. The reaction starts when the temperature reaches 420 F. Thetemperature of the reaction medium is permitted to rise until atemperature of about 475 F is reached. This normally takes some 1 to 3hours. It is desirable to reach 475 F- as soonas possible, while stillmaintaining sufficient control to prevent a reactor temperatureinstability. The temperature of the heat exchange medium is regulated bythe illustrated control system to maintain a reaction temperature of 475F. After reaching 475 F, the reaction is permitted to proceed for about4 hours at this temperature. During this 4 hour period, an additional260 pounds of the Na S-l.5H 0 are added at a relatively uniform ratethrough conduit 43. At the end of the 4 hour period, valve 49 is openedto dump the reactor.

While the invention has been described in conjunction with theproduction of polyphenylene sulfide for purpose of illustration, it isby no means limited to this reaction. In some con trol systems, the flowof more than one reactant can be adjusted by the computed productionrate signal. in some systems, timer 126 can be eliminated and thecontrol of reaction completion can be initiated when the signal /d0falls below a preselected set point value. Thus, while the invention hasbeen described in conjunction with a presently preferred embodiment, itobviously is not limited thereto.

What is claimed is:

1. A control system for a batch reactor with a heat exchanger havingheating medium inlet and outlet conduits associated therewith,comprising:

a first temperature sensing element connected to the inlet conduitadjacent the heat exchanger for sensing the temperature of the heatingmedium passing through said conduit;

a second temperature sensing element connected to the outlet conduitadjacent the heat exchanger for sensing the temperature of theheatingmedium passing through said conduit;

a flow measuring element associated with the outlet conduit formeasuring the flow rate of the heating medium discharging from the heatexchanger;

a first temperature transducer connected to the first temperaturesensing element for delivering a signal (T representative of themeasured temperature;

a second temperature transducer connected to the second temperaturesensing element for delivering a signal (T representative of themeasured temperature;

a differential temperature transducer connected to the first and secondtemperature transducers for receiving the signals (T and T therefrom,calculating the difference between said received signals, and deliveringa resultant signal representative of said calculated difference;

a flow transducer connected to the flow measuring element for deliveringa signal (F) representative of the measured flow rate;

a multiplying element connected to the differential temperaturetransducer and the flow transducer and having a set point K forreceiving the signals, multiplying the signals, multiplying the producttimes the set point K, and delivering a signal FK(AT) responsive to saidmultiplications;

an integrating element connected to the multiplying element forreceiving the signal FK(AT), integrating said signal, and delivering asignal representative of said integration;

a differentiating means connected to the integrating element forreceiving the integrated signal therefrom and delivering an outputsignal representative of the derivation of the integrated signal withrespect to time; and

means responsive to said output signal to control the operation of saidreactor to terminate a reaction therein when the reaction has beencarried out to a preselected degree of completion as measured by saidoutput signal.

2. The control system of claim 1, further comprising means responsive tosaidsecond signal to control the rate of addition of at least onereactant to said reactor.

3. The control system of claim 1 wherein said means to control includesa timing means actuated by said output signal of the differentiatingmeans, said timing means establishing a time signal at-a predeterminedtime interval after said timing means is actuated, said time signalbeing employed to control the operation of said reactor.

4. The control system of claim 1, further comprising a gate connectedbetween said differentiating means and said means to control, and meansresponsive to said integrated signal to open said gate when saidintegrated signal is of preselected

2. The control system of claim 1, further comprising means responsive tosaid second signal to control the rate of addition of at least onereactant to said reactor.
 3. The control system of claim 1 wherein saidmeans to control includes a timing means actuated by said output signalof the differentiating means, said timing means establishing a timesignal at a predetermined time interval after said timing means isactuated, said time signal being employed to control the operation ofsaid reactor.
 4. The control system of claim 1, further comprising agate connected between said differentiating means and said means tocontrol, and means responsive to said integrated signal to open saidgate when said integrated signal is of preselected magnitude.
 5. Thecontrol system of claim 1, further comprising first and second gates,each actuated by said integrated signal, said first gate being includedwithin said means to control the operation of said reactor to permitsaid means to control to operate when said integrated signal reaches apreselected magnitude, and further comprising means to control theintroduction of at least one reactant into said reactor, saidlast-mentioned means being actuated by said second gate when saidintegrated signal reaches a preselected magnitude.